The modern athletic shoe is a highly refined combination of many elements which have specific functions, all of which must work together for the support and protection of the foot during an athletic event. The shoe is divided into two general parts, an upper and a sole. The upper is designed to snuggly and comfortably enclose the foot. Typically, it will have several layers including a weather-and-wear resistant outer layer of leather or synthetic material such as nylon, and soft padded inner liner for foot comfort. Current uppers typically have an intermediate layer of a synthetic foam material. The three layers of the upper may be fastened together by stitching, gluing or a combination of these. In areas of maximum wear or stress, reinforcements of leather and/or plastic are attached to the upper.
The other major portion of the athletic shoe is the sole. Designed to withstand many miles of running, it must have an extremely durable bottom surface to contact the ground. However, since such contact may be made with considerable force, protection of the foot demands that the sole also perform a shock absorbing function. This shock absorbing function has been typically performed by a resilient, energy-absorbing material, which is located as a midsole between the durable lower surface material, i.e., the outer sole and the upper. This is particularly true for training or jogging shoes designed to be used over long distances and over a long period of time.
The outer sole has typically been designed to accomplish two functions, i.e., durability and traction. The capability of the outer sole as a contributing factor to shock absorbancy has generally been overlooked.
The outer sole design disclosed in U.S. Patent Application Ser. No. 178,088, filed on Aug. 14, 1980 and assigned to the assignee of the present application, took into consideration factors other than durability and traction. The structural design of the outer sole was related to a load analysis at the interface between the sole and the ground during running. The sole was then structured to minimize weight and maximize flexibility, while at the same time providing adequate durability, traction and stability. The design utilized transfer bars and ridges having varying widths and lengths. The ridges were located on the medial end lateral perimeter of the traction bars in the heel and forefoot section, and provided a slight cupping action.
A resilient shoe sole is disclosed in U.S. Pat. No. 3,100,354, issued on Aug. 13, 1963. The shoe sole in the '354 patent employs longitudinal rims along the lateral and medial sides of the sole interconnected by a thinner floor section. The lateral and medial rims are continuous and are not divided into traction elements and the outer sole appears to be connected directly to a shoe upper. The rims have an exemplary thickness of 3/4" and the floor section has an exemplary thickness 1/4". The '354 patent discloses that the thinner floor section cardles the foot so that the floor may largely conform to the foot structure.